1. Field of the Invention
The present invention relates to a method for manufacturing a glass ceramic multilayer substrate, and also relates to a glass ceramic multilayer substrate product obtained by using the manufacturing method. In detail, this invention relates to an improvement which can more reliably inhibit the undesired shrinkage that occurs in a sintering process for obtaining a glass ceramic multilayer substrate.
2. Description of the Related Art
When manufacturing a ceramic multilayer substrate having wiring conductors such as conductor film and via-hole conductor, the wiring conductors have to be subjected to sintering during the obtaining of the multilayer substrate. Accordingly, when a low resistance conductor such as Ag and Cu is used to form wiring conductors, the ceramic multilayer substrate has to be made of a material which can be sintered at a temperature equal to or lower than the melting point of Ag, Cu and the like. In order to meet such a requirement, a glass ceramic multilayer substrate has been put into actual use.
Usually, a glass ceramic multilayer substrate having wiring conductors formed by a low resistance conductor such as Ag, Cu may be manufactured in the following process. Namely, at first, a resin and a solvent are mixed into a powder mixture formed by a glass powder and a ceramic powder, so that a slurry is formed. This slurry is then formed into a plurality of sheets which can be used as green sheets. Subsequently, an electrically conductive paste containing an electrically conductive component which may be Ag or Cu is printed on the green sheets, thereby forming wiring conductors. Afterwards, a plurality of such green sheets each containing the wiring conductors are laminated one over another, thereby forming a laminated body which has not been sintered. Then, the laminated body is subjected to a sintering treatment, thereby obtaining the desired glass ceramic multilayer substrate.
However, the aforementioned sintering treatment has encountered the following problems. Namely, the shrinking behavior of the electrically conductive paste during the sintering process is different from that of the green sheets. Further, metal components contained in the electrically conductive paste will be dispersed into the glass material contained in the green sheets, and this will cause a change in the shrinking behavior of the glass material surrounding the wiring conductors. As a result, it is difficult to produce a glass ceramic multilayer substrate which is completely flat without any warpage.
Moreover, the sintering shrinkage of one glass ceramic multilayer substrate will not always be the same as that of another. This is because one batch of raw material can have a different quality from that of another, because the mixing ratio for making one group of green sheets can be different from the mixing ratio for making another group of green sheets, and further because the pressure for pressing one unsintered laminated body can be different from a pressure for pressing another unsintered laminated body. Under this circumstance, a conductor film formed on the outer surface of a glass ceramic multilayer substrate will often deviate from its correct position. As a result, the attachment size error will often go beyond an allowable range in a process where electronic parts are attached to a substrate in a manner as if flip chips are attached thereto, thus rendering it extremely difficult to ensure a high yield in an industrial production.
For this reason, it has long been demanded to provide an improved method for manufacturing an improved glass ceramic multilayer substrate, which method should satisfy the condition that when the sintering shrinkage in the plane direction of a glass ceramic multilayer substrate is small, and when its sintering process shrinking ratio (%) can be defined by the equation {(size before sintering)xe2x88x92(size after sintering)}xc3x97100/(size before sintering)}, the sintering process shrinking ratio is within 10%.
In order to meet the above requirement, Japanese Unexamined Patent Application Publication No. 4-243978 has suggested the following method for manufacturing an improved glass ceramic multilayer substrate. A plurality of green sheets each containing a glass powder and a ceramic powder as its solid components are laminated one above another to form an unsintered laminated body. Then, an arresting green sheet(s) containing as its solid component a ceramic powder which will not be sintered at a sintering temperature (this temperature is for sintering the unsintered laminated body) is/are laminated on one or both sides of the unsintered laminated body. If the sintering process is performed in such a state, it is possible to inhibit shrinkage in the plane direction of the laminated body, allowing a shrinkage only in the thickness direction, and thus producing a desired glass ceramic multilayer substrate having a high flatness. In this way, the above-described method makes it possible to manufacture a flat glass ceramic multilayer substrate.
However, the arresting green sheet(s) formed on one or both sides of the unsintered laminated body in the above-described method will have to be removed after the sintering process is over. Such green sheet(s) will not form part of the laminated product. Because of this, the total cost for manufacturing a glass ceramic multilayer substrate is high, since the entire manufacturing cost will include a cost for forming the arresting green sheet(s) and also a cost for removing the arresting green sheet(s).
In view of the above, one of the most noticeable techniques during the last several years was suggested in Japanese Unexamined Patent Application Publication Nos. 6-97656 and 6-172017. These patent publications disclose a method which involves a sintering process, but which employs first green sheets having a certain shrinking behavior and second green sheets having a different shrinking behavior from that of the first green sheets. According to this method, it is possible to inhibit shrinkage in the plane direction of the laminated body by sintering an unsintered laminated body formed by laminating these green sheets, thereby making it possible to produce a flat glass ceramic multilayer substrate.
The basic technical principles disclosed in the above patent publications may be stated as follows.
When a sintering process is first carried out at a relatively low temperature corresponding to a sintering temperature for sintering the first green sheets, the first green sheets will tend to shrink. However, since the sintering temperature at this time is lower than the sintering temperature for sintering the second green sheets, the second green sheets will be kept in an unsintered state, thus having almost no shrinkage. For this reason, the shrinkage in the plane direction of the first green sheets can be inhibited by an arresting action of the second green sheets. Then, once another sintering process is carried out at a relatively high temperature corresponding to a sintering temperature for sintering the second green sheets, the second green sheets will tend to shrink. At this time, the shrinkage in the plane direction of the second green sheets will be inhibited by an arresting action of the sintered first green sheets. In this way, the sintering shrinkage of the laminated body is greatly inhibited so that it occurs only in the thickness direction of the laminated body, with almost no shrinkage occurring in the plane direction thereof. As a result, it is possible to produce an improved glass ceramic multilayer substrate having a reduced shrinkage and an increased flatness.
However, the glass ceramic multilayer substrate manufacturing method disclosed in Japanese Unexamined Patent Application Publication Nos. 6-97656 and 6-172017 also has a problem that in carrying out the process disclosed in these patent publications, it will sometimes be difficult to sufficiently inhibit shrinkage in the plane direction of a laminated body during the sintering process, and it will also be occasionally difficult to ensure that a sintering shrinkage can be controlled within 10%. It is difficult to exactly produce an improved glass ceramic multilayer substrate having a sufficient flatness.
The above troubles are associated with the difference between a shrinkage ending temperature of one group of green sheets and the shrinkage starting temperature of the other group of green sheets, and also related to a temperature rising speed in the sintering process. Further, it has been found that the above troubles happen early if there is only a small difference between the shrinkage ending temperature of one group of green sheets and the shrinkage starting temperature of the other group of green sheets, and also if the temperature rising speed is high in the sintering process.
In order to avoid the above troubles, one may consider inhibiting shrinkage in the plane direction of a laminate body by providing a portion in the laminated body which is to be sintered at a predetermined temperature within an intermediate temperature range existing between the shrinkage ending temperature of one group of green sheets and the shrinkage starting temperature of the other group of green sheets, or by slowing down the temperature rising speed. However, this will require a longer operation time for completing the sintering treatment and thus not advisable in view of a increased costs.
Accordingly, it is an object of the present invention to provide an improved method for manufacturing a glass ceramic multilayer substrate, such that even if the temperature rising speed during sintering is increased, it is still possible to exactly inhibit shrinkage in the plane direction of a laminated body. It is another object of the present invention to provide an improved glass ceramic multilayer substrate obtained by using the method of the present invention.
The glass ceramic multilayer substrate manufacturing method according to the present invention comprises a step (hereinafter sometimes referred to as a first step) of preparing first green sheets each containing as its solid components, a first glass powder and a first ceramic powder; a step (hereinafter sometimes referred to as a second step) of preparing second green sheets each containing as its solid components, a second glass powder and a second ceramic powder and capable of exhibiting a sintering shrinkage different from that of the first green sheets; a step (hereinafter sometimes referred to as a third step) of forming conductor films and/or via-hole conductors in the first green sheets and/or the second green sheets; a step (hereinafter sometimes referred to as a fourth step) of forming an unsintered laminated body by laminating together at least one of the first green sheets and at least one of the second green sheets; and a step (hereinafter sometimes referred to as a fifth step) of sintering the laminated body. The method is characterized by the following aspects which are effective for solving the aforementioned problems peculiar to the above-described conventional methods.
After the unsintered laminated body has exceeded the lower one of the respective glass transition temperatures of the first and second glass powders in the fifth step in the method of the present invention, the unsintered laminated body is caused to reach the highest sintering temperature through a temperature rising process having a temperature rising speed of Xxc2x0 C./min (X greater than 1), thereby effecting a predetermined sintering treatment to occur with a predetermined sintering profile.
Further, if the shrinkage starting temperatures (xc2x0 C.) of the first and second green sheets are TSa and TSb in the fifth step, and if the sintering process ending temperatures (xc2x0 C.) (when a shrinkage is 90% of a predetermined shrinking amount) of the first and second green sheets are TFa and TFb, the conditions should be set to satisfy the following equation.
(TFa+3X) less than TSb or (TFb+3X) less than TSa 
Namely, the glass ceramic multilayer substrate manufacturing method according to the present invention is characterized in that conditions are set which satisfies the equation (TFa+3X) less than TSb or (TFb+3X) less than TSa. In order to satisfy this condition, it is required to properly select the materials forming the first and second green sheets, or set an appropriate temperature rising speed. However, it is also possible that the above condition may be satisfied by designing proper materials for the first and second green sheets and at the same time setting an appropriate temperature rising speed.
When considering proper materials for the first and second green sheets in order to satisfy the above condition, another aspect of the present invention is to prepare the first and second green sheets using a method capable of rendering the prepared sheets to satisfy the above condition. For this purpose, the glass ceramic multilayer substrate manufacturing method according to the present invention is carried out by including the following preparation steps.
Namely, the glass ceramic multilayer substrate manufacturing method of the present invention, in accordance with its another aspect, comprises preparing first test green sheets each containing a first glass powder and a first ceramic powder as its solid components; preparing second test green sheets each containing as its solid components, a second glass powder and a second ceramic powder and capable of exhibiting a sintering shrinkage different from that of the first test green sheets; measuring the shrinking amounts of the first and second test green sheets, while at the same time sintering in accordance with a predetermined sintering profile so as to enable the green sheets to reach the highest temperature through a temperature rising process having a temperature rising speed of 1xc2x0 C./min; seeking the shrinkage starting temperatures TSa (xc2x0 C.) and TSb (xc2x0 C.) of the sintering process, and also seeking the sintering process ending temperatures TFa (xc2x0 C.) and TFb (xc2x0 C.); and confirming whether or not the first and second test green sheets satisfy the equation (TFa+3X) less than TSb or (TFb+3X) less than TSa.
The glass ceramic multilayer substrate manufacturing method of the present invention further comprises preparing first green sheets which are the same as the first test green sheets; preparing second green sheets which are the same as the second test green sheets; forming conductor films and/or via-hole conductors in the first green sheets and/or the second green sheets; and forming an unsintered laminated body by laminating at least one of the first green sheets and at least one of the second green sheets. After the unsintered laminated body has exceeded the lower one of the respective glass transition temperatures of the first and second glass powders, the unsintered laminated body is caused to reach the highest sintering temperature through a temperature rising process having a temperature rising speed of Xxc2x0 C./min (X greater than 1), thereby effecting a desired sintering treatment in occurrence with a predetermined sintering profile.
It is preferable in the present invention that the thermal expansion difference between the first green sheets and the second green sheets is an average thermal expansion coefficient in a temperature range from 20xc2x0 C. to the lower one of the respective glass transition temperatures of the first and second glass powders, and is preferable to be controlled within xc2x10.5xc3x9710xe2x88x926/xc2x0 C.
In order to ensure that the first green sheets exhibit a sintering shrinkage different from that of the second green sheets, it is required to satisfy at least one of the flowing three conditions. A first condition (A) is that the first glass powder has a composition different from that of the second glass powder. A second condition (B) is that the first ceramic powder has a composition different from that of the second ceramic powder. A third condition (C) is that the mixing ratio of the first glass powder to the first ceramic powder in the first green sheets is different from the mixing ratio of the second glass powder to the second ceramic powder in the second green sheets. If the third condition is satisfied, the first glass powder may have the same composition as the second glass powder, and the first ceramic powder may have the same composition as the second ceramic powder.
It is preferable in the above fourth step that one of the first and second green sheet groups are laminated to form an inner layer, and the other of the first and second green sheet groups are laminated to form outer layers, with each inner layer and each outer layer being formed by at least one green sheet.
As a preferred embodiment of the present invention, the first glass powder is BaOxe2x80x94MgOxe2x80x94SiO2xe2x80x94B2xe2x80x94O3 glass, and the first ceramic powder is at least one of alumina, spinel and zirconia. The first green sheets are so formed that the mixing ratio of the first glass powder to the first ceramic powder is about 40:60 to 100:0 by weight. The first glass power may contain at least one substance selected from the group consisting of Al2O3, ZnO, TiO2, ZrO2 and R2O (R is an alkali metal) as an additive. Moreover, each of the first green sheets may contain copper oxide.
Further, as a preferred embodiment of the present invention, the second glass powder is MgOxe2x80x94ZnOxe2x80x94SiO2xe2x80x94B2O3 glass, and the second ceramic powder is BaOxe2x80x94Re2O3xe2x80x94Nd2O3xe2x80x94TiO2 (Re is a rare earth element). The second green sheets are so formed that a mixing ratio of the second glass powder to the second ceramic powder is about 10:90 to 40:60 by weight. The second glass powder may contain as an additive at least one substance selected from the group consisting of BaO, CaO, Al2O3 and R2O (R is an alkali metal). Moreover, each of the second green sheets may contain copper oxide.
According to the glass ceramic multilayer substrate manufacturing method of the present invention, when a sintering shrinkage ratio (%) is defined by the equation {(size before sintering)xe2x88x92(size after sintering)}xc3x97100/(size before sintering), the sintering shrinkage ratio of the laminated body at the fifth step is preferably within 10%.
In addition, the present invention is also directed to an improved glass ceramic multilayer substrate obtained by using the manufacturing method described above.